After this length of time, it's quite hard to tell quite how much involvement Heuer had in final assembly of these without getting some inside information. Obviously, lots of Heuer parts but then those "Heuer" parts came from lots of different suppliers so they could be forwarded on elsewhere for assembly. Given that there were a number of customers taking similar watches though, I guess it's quite possible that Heuer watchmakers were doing final assembly for these, the Dugenas etc.

Have you seen the back of the dial? The Carrera Cal 15 dials were made by Singer (whose dials typically have a swan (or many swans) stamped on the obverse) but I'm not sure for the other models. So in one sense, that Bulova dial isn't any less a Bulova part than a Heuer dial made by Singer is a Heuer part.